(ORDO NEWS) — A gene associated with hearing development in humans has just been linked to sensory development in sea anemones.
The gene, called pou-iv (pow-four), can be found in the tentacles of the stargazer sea anemone (Nematostella vectensis), where it plays an important role in the development of the sense of touch in animals.
Cnidaria, the phylum to which sea anemones belong, is the closest relative of Bilateria, bilaterally symmetrical animals like humans, and descended from their last common ancestor around 748-604 million years ago.
The discovery of the role of this gene in the stargazer sea anemone suggests that it was present in their common ancestor and probably played a role in the development of the sense organs even then.
“This study is exciting because it not only opens up a new field for studying how mechanosensation develops and functions in the sea anemone… but also tells us that the building blocks of our sense of hearing have ancient evolutionary roots dating back hundreds of millions of years to Precambrian,” said biologist Nagayasu Nakanishi of the University of Arkansas.
In humans and other vertebrates, the receptors in the auditory system are called hair cells. These cells have bundles of finger-like organelles called stereocilia that sense mechanical stimuli, namely vibrations that we hear as sound. In mammals, pou-iv is essential for hair cell development; we know this because mice in which pou-iv has been removed become deaf.
The starfish sea anemone has similar mechanosensory hair cells on its tentacles that are used to sense movement. However, little was known about the anemone pou-iv gene and what role, if any, it plays in the development of the sensory system.
A group of researchers led by biologist Ethan Ozment of the University of Arkansas set out to find out what this gene does. The best way to do this is to turn off the gene with the CRISPR-Cas9 gene editing tool and observe the changes. That is exactly what the team did.
They injected a cocktail containing the Cas9 protein into fertilized star sea anemone eggs to cut out the pou-iv gene and studied developing embryos as well as grown mutated star anemones.
Compared to wild-type control anemones, the mutant animals showed abnormal development of tentacle hair cells and were unresponsive to touch. Without pou-iv, anemones could not perceive mechanical stimuli through their hair cells.
In addition, pou-iv knockout in anemones significantly downregulated a gene very similar to that produced by polycystin 1 found in vertebrates, where it is needed to determine fluid flow in the kidneys. Sea anemones may not have buds, but the ability to sense fluid flow would be useful for marine animals.
According to the researchers, the findings suggest that pou-iv played a role in the development of mechanosensory cells in the common ancestor of Cnidaria and Bilateria. However, in order to trace the gene even further, data from other phyla with earlier points of divergence would be needed.
“Our results indicate that the role of pou-iv in mechanoreceptor development is broadly conserved among Cnidaria and Bilateria,” the researchers wrote in their paper.
“How early the role of pou-iv in mechanoreceptor differentiation arose in animal evolution remains unresolved and requires comparative data from placosoids and sponges, which are not yet available.”
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